Optical frequencies afford much greater communication data rates. The emergence of fiber optic waveguides and optoelectronics has enabled the optical communications industry to make great advances, however at a generally higher cost than that of well-established radio and microwave frequency communication systems. The interface between the electronics and the fiber waveguide is one area in which precision is required, but manufacturers in the optical communications industry are constantly seeking to effect highly precise interconnects at a low cost of manufacture. The emergence of silicon waferboard technology enables great precision in aligning the fiber to the device. This technology is emerging in the industry as a vehicle for low cost-high precision optical interconnects. One method of effecting accurate passive alignment between a device and a fiber or a fiber and a fiber, is the use of V-shaped grooves which are etched into the silicon substrate. The v-grooves are the crystalline planes of silicon revealed by etching the silicon by known techniques. As is disclosed, for example, in U.S. Pat. Nos. 5,224,782; 5,163,108; 5,077,878 and 5,182,782, incorporated herein by reference, by etching along preferred crystalline planes in a silicon waferboard, v-shaped grooves are formed for the accurate passive alignment between fibers or between fibers and devices. For example, as disclosed in U.S. Pat. No. 4,210,923 to North, et al., an SiO.sub.2 mask is applied on a silicon substrate having a major surface in the (110) crystalline orientation. By application of a solution of KOH and water, anisotropic etching is effected and v-grooves are formed having sidewalls in the (111) family of crystalline planes. As is further disclosed in North, et al., the precise dimensions of the etched grooves are controlled by picking the width of the etch. Thereby, due to known characteristic relative angles of the crystalline planes, the accurate passive alignment of a fiber to a device is achieved. To be sure, the use of the characteristic planes of a crystalline material can be used to effect a variety of apertures, grooves and the like in crystalline materials thereby allowing a great deal of methods to achieve accurately aligned optical interconnection. Other examples of masking and etching monocrystalline materials to reveal, at desired locations, grooves .and or apertures with side walls in preferred crystalline directions are disclosed in U.S. Pat. Nos. 4,897,711; 4,779,946 and 4,446,696, incorporated herein by reference. Another example of the use of silicon waferboard technology to effect interconnection between a fiber waveguide and an optoelectronic device is disclosed in U.S. Pat. No. 4,897,711 to Blonder, et al., incorporated herein by reference. V-shaped grooves defined by crystallographic planes are etched in silicon by processes well known in the art, and optical fibers are placed in a position to receive an optical signal from an optoelectronic device. Blonder, et al. discloses the deposition of a reflective coating on a crystallographic plane revealed by etching the silicon, as well etching a hole in a section of silicon to secure and align a ball lens for focusing light reflected off the reflective coating into a fiber mounted in a v-groove. The reflective coating enables the optical signal to impinge on the fiber within its acceptance angle. The planes revealed in the etching process are characteristic of silicon, and accordingly, are of well known orientation. The '711 reference discloses the use of the precision of the orientation of the crystalline planes to effect the accurate passive alignment of the device to the fiber via the reflective surface.
As stated, one of the great advantages of using silicon waferboard technology as an optical interconnect is the ability to accurately align optical transmission media at interconnection points. One way that this has been achieved is by the use of precision microspheres as is disclosed in U.S. Pat. No. 5 123,073, incorporated herein by reference is an example of the use of the alignment spheres. The basic principle disclosed is the etching of the silicon waferboard to reveal inverted pyramidal shaped recesses which receive the spheres in one half of the silicon waveguide coupler. The recesses are placed precisely on the substrate of silicon, and are sized so that roughly one-half of the sphere protrudes above the surface of the substrate. The second half of the coupler is also a silicon substrate with precisely defined inverse pyramidal shaped recesses which are aligned with the recesses of the first half of the coupler. The recesses in the second half of the coupler receive the protruding portion of the complimentary spheres of the first coupler and thereby enable an accurate passive alignment between two halves of an optical coupler.
The advent of the use of optical frequencies as means of communications has lead to a great deal of interest in the past few decades to new ways of developing optical transceivers and means to effect optical interconnects. One of the areas of great interest has been to effect multiplexing and demultiplexing at optical frequencies in fiber optic waveguides. While optoelectronic devices have been developed to effect multiplexing (mux) and demultiplexing (demux), less complex means have been developed to effect these desired results. For example, U.S. Pat. No. 5,107,359 to Ohuchida, incorporated herein by reference, discloses the use of holographic lenses which in combination with a second hologram that acts as a reflective surface or holographic lens and a reflective surface effects demux by making use of the frequency dependance of a spatial diffraction grating to separate two or more signals of differing wavelengths from a single fiber and to reintroduce the separated signals into separate fibers. Multiplexing is obviously the implementation of the same components with signal direction reversed, whereby two signals of differing frequencies from two fibers are combined to travel in the same fiber.
The interconnection of optical signals often requires a manipulation of the light beam to effect a desired result. Be it interfacing the signal from a fiber to a detector, or changing the direction of propagation of light to effect coupling of light to one or more waveguide(s), silicon waferboard technology enables accurate passive alignment to enable coupling of active and/or passive devices to fibers. It is desirable to be able to effect a simple, low cost mux/demux of the optical signal as well as to effect coupling of the optical signals between fibers in a simple low cost apparatus that is integral with the multiplexer/demultiplexer. Finally, highly accurate passive alignment of the optical fibers is essential to the coupling and mux/demux.